It is known that the temperature of the hydraulic fluid in a hydraulic device increases during operation. This applies particularly to hydraulic travel drives with a closed hydraulic circuit formed by a driven variable-displacement pump and a hydraulic motor connected to the latter by a feed line and a return line. The increase in the temperature of the hydraulic fluid has an effect on the hydraulic motor and is reflected in a significant increase in the temperature of the motor casing. It is therefore extremely advantageous to flush the hydraulic motor with cooler hydraulic fluid. This makes it possible to avoid a situation where the hydraulic motor reaches its limit temperature in continuous operation, thereby increasing its life.
One known solution for flushing the hydraulic motor with cool hydraulic fluid is to pass an additional line from the tank for the hydraulic fluid to the hydraulic motor. The hydraulic fluid in the tank is at a lower temperature than the hydraulic fluid in the closed hydraulic circuit. The structural implementation of this known method involves a large outlay on construction since it is necessary to pass an additional flushing line to the hydraulic motor, which is often very remote.
According to the prior art, a flushing valve has also already been inserted into the hydraulic motor, this valve diverting flushing oil from the respective lower pressure line of the high-pressure circuit in order to implement the method mentioned at the outset. However, it is often impossible to accommodate a flushing valve in the motor for structural reasons. In this case, it is necessary to have recourse to xe2x80x9ccross-flushingxe2x80x9d, which likewise requires additional lines.
The prior art also includes hydraulic motors for driving by means of hydraulic fluid, with a braking device, which has a connection for a brake release line and is constructed in such a way that the braking action is canceled when the braking device is subjected to the pressure or a control fluid via the brake release line.
Hydraulic motors for driving by means of hydraulic fluid, with a braking device which has a connection for a brake release line and is constructed in such a way that the braking action is canceled when the braking device is acted upon by the pressure of a control fluid via the brake release line, are known. If the additional flow of hydraulic fluid flushing the casing of the hydraulic motor is passed into the braking device of the hydraulic motor when a hydraulic motor of this kind is provided, it is possible, by appropriate configuration of the braking device, to ensure that although, on the one hand, the braking action of the braking device is canceled, the additional flow of hydraulic fluid acting upon the braking device is, on the other hand, passed as a continuous flow through the casing of the hydraulic motor. This means that only a single additional flow of hydraulic fluid need be passed to the hydraulic motor, and it is thus only necessary to use a line which is already present in any case, namely the control line for the braking device, for an additional task.
It is therefore a principal object of this invention to provide a method for flushing the casing of a hydraulic motor, and of creating a hydraulic motor and a hydraulic drive, by means of which the casing of the hydraulic motor can be flushed in an effective manner and hence protected from an excessive increase in temperature without the need for a high outlay on construction.
These and other objects will be apparent to those skilled in the art.
The invention relates to a method for flushing the casing of a hydraulic motor with hydraulic fluid, the hydraulic motor being driven by hydraulic fluid which flows through and its casing being flushed with an additional flow of the hydraulic fluid, the temperature of which is lower than that of the hydraulic fluid that drives the hydraulic motor. The invention also relates to a hydraulic motor, a hydraulic drive and the use thereof.
The method of this invention is achieved by virtue of the fact that the additional flow of hydraulic fluid which flushes the casing of the hydraulic motor simultaneously acts on the braking device of the hydraulic motor in the sense of canceling the braking action.
In this invention provision is made for the additional flow of hydraulic fluid to pass through a restriction when it leaves the braking device, and for the restricted flow to pass through the casing of the hydraulic motor as a continuous flushing flow. Appropriate dimensioning of the restriction makes it possible to achieve the correct compromise between a sufficiently high effective pressure within the braking device to cancel the braking action, on the one hand, and a sufficiently strong flushing flow for the casing of the hydraulic motor, on the other hand.
Although the hydraulic fluid in the tank is already at a lower temperature in any case than, for example, the hydraulic fluid in the hydraulic circuit of a travel drive, the cooling effect can be improved even further, in accordance with a further refinement of the method, if, after leaving the casing of the hydraulic motor, the flushing flow is passed through a cooler and only then into the reservoir for the hydraulic fluid.
According to further advantageous refinements, structural implementations of the restriction present in the hydraulic motor according to the invention can comprise a preloaded non-return valve, a pressure-limiting valve or a nozzle. The hydraulic motor according to the invention fits well into known hydraulic drives if, according to an additional development, the outlet opening of the casing of the hydraulic motor is designed for connection to a leakage-oil line, which leads in the customary manner to the tank for the hydraulic fluid. A particularly advantageous development of a hydraulic drive of this kind consists in that the braking device is connected by a brake release line to a shut-off device which also enables and interrupts the supply of hydraulic fluid to the servo adjustment system of the variable-displacement pump, and that the outlet opening of the casing of the hydraulic motor is connected to the tank for the hydraulic fluid by a leakage-oil line. This keeps the outlay on construction particularly low because, of course, the shut-off device for the servo adjustment of the variable-displacement pump is present in any case and the release of the braking device must take place simultaneously with adjustment of the variable-displacement pump in any case. This ensures that the abrasion from the braking device is also fed to the filter system, and it is clear that the braking device too is cooled continuously by the relatively cold hydraulic fluid used exclusively for control.
In an expedient refinement of the hydraulic drive, provision is furthermore made for a cooler, which is connected to the leakage-oil line, to be arranged between the casing of the hydraulic motor and the tank for the hydraulic fluid.
The hydraulic drive according to the invention is suitable for many applications in which a significant increase in the temperature of the hydraulic fluid can be expected in continuous operation, e.g. in machines. However, the preferred use of the hydraulic drive according to the invention is as a travel drive in road and rail vehicles.